Diagnosis
The LED itself rarely fails. The issue is usually a disconnected wire or damaged solder joint from vibration.
How to Fix It
Remove the battery. Look into the light port above the trigger. Check for visible debris blocking the LED. Use a toothpick to gently clear it. If clear, the internal wire at the LED board is likely broken.
If That Didn't Work
The problem could be at the switch/control board connection. This requires disassembly to inspect.
Heads Up
Do not poke the LED lens with metal. You can scratch or crack the silicone waterproof seal.